Deputy Speaker Nigel Evans was recently cleared of sex charges – but his case has exposed a dark side of Westminster where drink-fuelled MPs make passes at young staff.

Lucille Harvey, of the Unite union’s Parliamentary branch, said those who stood up to MPs were threatened with having their careers ended.

She added: “We have had instances where staff have been told ‘I will ruin you’.”

One alleged victim claimed last night: “A lot of MPs think they have almost got a right to try it on with junior staff, male or female.

“They are almost affronted if the staff don’t go along with it.”

Now senior Tories fear they could be engulfed by a new series of scandals which can only boost UKIP’s prospects ahead of May’s local and European elections.

MP Patrick Mercer faces suspension when watchdogs deliver their verdict after he was caught in an alleged lobbying sting.

And fellow backbencher Peter Bone is having his expenses probed in a new blow to the PM , who is desperate to move on from the expenses scandal that cost Culture Secretary Maria Miller her Cabinet job.

Revelations: Mark Menzies MP (Photo: John Gladwin)

Dozens of researchers and other young staff told a Channel 4 News investigation that they had been subjected to harassment and unwanted advances.

The BBC is also probing claims that sexual bullying is rife in Parliament.

A small circle of gay Tory MPs are said to have pestered young male staff.

One allegedly boasted that sexual favours from a worker in his office was an “unwritten part of the contract”.

Another is said to have told a female who complained of harassment by a party donor to “woman up”.

There are even rumours a senior Tory has been accused of date rape by another man.

Tory MP Margot James has warned an independent body may be needed to police Parliamentary conduct.